Hydraulic pit prop or jack



July 26, 1955 D. G. SUTTON HYDRAULIC PIT PROP OR JACK 2 Sheets-Sheet 1 Filed Sept. 20, 1954 INVENTOR DUDLA'Y 6, SUTTON BY v;

ATTORNEYS July 26, 1955 D. s. SUTTON HYDRAULIC PIT PROP QR JACK 2 Sheets-Sheet 2 Filed Sept. 20, 1954 Fit-3.2%

INVENTOR DUDLEY 6 SUTTON AT'TORNEYS United States Patent HYDRAULIC PIT PROP OR JACK Dudley G. Sutton, Cheltenham, England, assignor to Dowty Auto Units Limited, Cheltenliam, England Application September 20, 1954, Serial No. 457,037

Claims priority, application Great Britain September 24, 1953 4 Claims. (Cl. 60-52) This invention relates to hydraulic jacks of a special type and for use in mine pits, termed pit props, in which a hollow cylindrical ram, intended to be upright when the prop is in use, constitutes a reservoir for hydraulic liquid and is slidable telescopically with respect to an external cylinder so that extension of the prop can be effected by operation of a pump situated in the ram to cause liquid to pass from the reservoir into the pressure chamber formed by the cylinder space beyond the inner end of the ram, and contraction of the prop can be effected when desired under the control of an externally operable release valve in a return communication between the pressure chamber and the reservoir. The invention, moreover, relates to hydraulic pit props in which the release valve is situated adjacent the outer end of the ram and communicates with the cylinder space along a conduit which extends down from the valve and through the inner end of the ram, as disclosed in U. S. A. patent specification No. 2,621,631. Such pit props are hereinafter referred to as hydraulic pit props of the kind hereinbefore specified.

The object of the present invention is to provide an improved construction of hydraulic pit prop of the kind hereinbefore specified, and to this end and in accordance with the invention, the conduit which extends between the cylinder space beyond the inner end of the ram and the release valve situated adjacent the outer end of the ram is disposed coaxially of the tube of the ram, and the pump comprises large and small area pistons arranged concentrically between the valve conduit and the ram tube, and means for rendering said large area piston ineffective upon the attainment of a predetermined pressure in the cylinder space.

The valve conduit preferably forms a guide stern for a tube which fits at its inner end into a cylinder upstanding from the closure member at the inner end of the ram and which constitutes the small area piston of the pump. The large area piston of the pump is preferably in sliding engagement with the inner surface of the tube of the ram and has clearance around the tube of the small area piston and operates between shoulders on said tube. Both pistons are preferably reciprocable by a tubular driving member extending around the valve conduit to a slide block at the upper end of said conduit, said slide block being in pin-and-slot driving connection with a rotary crank arm.

A hydraulic pit prop in accordance with the preferred embodiment of the invention will now be described with reference to the accompanying drawings, of which:

Figure 1 shows the prop in longitudinal sectional elevation;

Figure 2 is a transverse sectional view of a detail of Figure l; and

Figure 3 is a fragmentary sectional view taken on the line III-III of Figure l.

The pit prop comprises two main parts, namely an upper part or ram indicated generally at 11, and a lower 2,713,773 Patented July 26, 1955 ice part or cylinder 12 into which the ram 11 telescopes in sealed relation with the cylinder 12. The ram 11 is closed at its upper end by a head piece 13 for engagement with the mine roof, and the cylinder 12 is closed at its lower end by a foot piece 14 for engagement with the floor of the mine. The ram 11 has an end closure member 15 which operates as a piston in the cylinder 12 and which carries a sealing gland 16 around its periphery. The ram 11 constitutes a reservoir for hydraulic liquid and incorporates a pump, to be described, by which liquid can be transferred from the reservoir into the cylinder space 17 beyond the inner end of the ram to bring about extension of the prop. When the prop is to be withdrawn from service, contraction of the prop is brought about by the opening of a release valve in a return communication between the cylinder space 17 and reservoir, also to be described. I

The ram 11 comprises a tubular part 18 and a tubular part 19 of larger diameter than the tubular part 18, and an annular shoulder 20 joining the two parts 18 and 19 together in co-axial relationship. The enlarged size of the tubular part 19 gives a useful added volumetric capacity to the reservoir space in the ram 11.

A valve housing 21 extends transversely through the ram 11 adjacent the upper end of the tubular part 19 to which said housing is permanently secured. The housing 21 has a radial port 22 disposed centrally of the ram and communicating with the cylinder space 17 beyond the inner end of the ram by a tube 23 which is secured at its upper end to the housing 21 and which extends through the end closure member 15 of the ram 11. The tube 23 is co-axial .with respect to the tubular parts 18 and 19. The closure member 15 is secured at the inner end of the ram 11 by a nut 24 screwed on to the end of the tube 23, and has sealing rings 25 and 26 by which it is sealed to the tubular part 18 and tube 23 respectively. The nut 24 also serves to retain a flanged end plate 27 which holds the sealing gland 16 on the closure member 15. Anon-return valve 28 is provided in the inner end of the tube 23 and operates to prevent flow from said tube into the cylinder space 17. The tubular part 18 of the ram 11 is a sliding fit in a bearing bush 29 secured in the upper end of the cylinder 12. Above the bearing bush 29, the cylinder 12 is fitted with a wiper ring 30 for preventing dust and moisture from passing down around the ram 11.

The valve housing 21 also has a radial port 31 opening into the reservoir space in the ram 11, and communication between the housing ports 22 and 31 is by way of a central passage 32 in said housing under the control of a release valve 33, or by way of said passage 32 and additional passages 34 and 35 under the control of a relief valve 36. The relief valve 36 is loaded by a spring 37 in a casing 38 to determine the blow-01f pressure of the valve and thus to limit the pressure which can be built up in the cylinder space 17. The release valve 33 constituted by the casing 38 is loaded by a spring 39 which normally holds the release valve 33 in sealed engagement with the step 44 in the valve housing 21. The casing 38 housing the relief valve 36 and constituting the release valve 33 has a central threaded extension 41 screwed into a plunger member 42 which is sealed at 43 with respect to a bore 44 in the housing 21. The plunger member 42 is adapted to be engaged by a manually operable external cam member .5 fast with a loop 46. When the loop is swung out and up from the position shown in Figure l, the cam 45 engages the plunger member 42 to displace the release valve 33 and establish communication between the ports 22 and 31 of the valve housing. This will place the cylinder space 17 in communication with the reservoir regardless of the pressure prevailing in said cylinder space. The spring 39 need not be particularly strong and need not be related to the strength of the spring 37 because the pressure acting in the central passage 32 and tending to unseat the release valve 33 also acts oppositely on the slightly larger area of the plunger member 42 and tending to hold the release valve in the closed position. The action of the pressure liquid therefore biases the release valve 33 in the closing sense. Although not shown, an air breather valve may be provided in the upper end of the ram 11 above the level of liquid therein.

The pumping means by which liquid is transferred from the reservoir into the cylinder space 17 will now be described. The closure member at the inner end of the ram 11 has an upstanding cylindrical wall 47 forming an annular cylinder space 48 around the lower end of the tube 23. The lower end of a tube 49 surrounding the tube 23 and guided by the latter projects into the cylinder space 48. A sealing ring 50 serves to prevent escape of liquid from the cylinder space 48 between the upstanding cylinder 47 and the tube 49. The tube 49 has an extension 51 somewhat spaced around the tube 23 and secured to a slide block 52 on the upper end of the tube 23. The slide block 52 and with it the tubes 51 and 49 are adapted to be reciprocated from a crankshaft 53 having a crank arm 54 and a crank pin 55 operating in a transverse slot 56 in the slide block 52, see Figure 2 in which the crank arm is seen in the dead centre position. The crankshaft 53 has a squared end 57 for driving engagement with a suitable handle. The shaft end 57 is surrounded by a protecting shroud 58. The cylinder space 48 forms a high pressure pumping chamber by virtue of non-return valves 59 and 60. When the tube 49 is raised in the cylinder space 48, liquid enters said space from the reservoir across the non-return Valve 59, and when the tube 49 is lowered into the cylinder space 48, the liquid in said space is forced out across the non-return valve 60 into the cylinder space 17. This pump will transfer a small quantity of liquid from the reservoir into the cylinder space 17 for each stroke of the pump handle, and is capable of being operated up to the desired setting pressure in the prop.

In order that extension of the prop into engagement with the mine roof may be effected rapidly, there is provided also a large diameter pump capable of transferring a large quantity of liquid at low pressure for 1;

each stroke of the pump handle. For this purpose, there is provided an annular piston 61 which fits within the tubular part 18 of the ram 11 and operates as a clack valve between shoulders 62 and 63 on the tube 49. The distance between the shoulders 62 and 63 slightly exceeds the axial dimension of the piston 61, and the piston 61 has an annular clearance space 64 around the tube 49. When the tube 49 is moved in a downward direction, the shoulder 62 engages the upper side of the piston 61 and closes the annular space 64 so that liquid in the ram 11 and below the piston 61. will be trans ferred through non-return valves 65 in the closure member 15, see Figure 3, and into the cylinder space 17. During upward movement of the tube 49, the shoulder 62 moves away from the piston 61 so that there is now a passage for liquid across the piston 61 and over parts of the shoulder 63 to enable liquid to charge the space below the piston 61 and also the cylinder space 48. The piston 61 is fitted with a relief valve 66 which limits pressure below said piston, the valve 66 controlling communication between an inlet opening 67 and spaced outlet openings, one of which is indicated at 68.

The prop is used in the following manner. Operation of the pumping means by the handle will bring about a rapid extension of the prop by means of the piston 61 which is designed to give a large flow at low pressure. When the head piece 13 of the prop meets the resistance of the mine roof, the pressure in the cylinder space 17 and below the piston 61 will rise until the relief valve 67 blows to render the piston 61 of the pump ineffective.

till

The high pressure piston constituted by the lower end of the tube 49 continues to pump small quantities of liquid until the necessary setting pressure has been created in the cylinder space 17. After this and during the time the prop is serving as a roof support, there is a tendency for the roof weight to increase and place a greater loading on the prop. This loading is limited by the action of the relief valve 36 in the return communication between the cylinder space 17 and the reservoir. It will be appreciated that the space inside the tube 23 forms part of the pressure chamber of the prop. The prop therefore gradually shortens in a controlled manner with increasing roof loading.

When the prop is to be withdrawn from service, a cord or cable is attached to the loop 46 so that an operator standing a safe distance away from the point of support can, by pulling on said cord or cable, unseat the release valve 33 to open the cylinder space 17 to the reservoir to allow the prop to shorten and thereafter, by continuing to pull on the cord or cable, cause the prop to topple over and be dragged endwise towards him. Any tendency for air in the upper part of the reservoir to pass down through the tube 23 into the cylinder space 17 during the withdrawal of the prop is countered by the closing of the non-return valve 28 in said tube.

The construction of the pit prop above described enables the release valve to be situated conveniently at the upper end of the prop, and makes provision for the employment of a double-area pump of the two-stage type giving the maximum rate of prop extension. The features of the tube 23 and double-area pump 61, 49 are thus combined in a simple and efficient manner.

I claim as my invention:

1. A hydraulic pit prop comprising an outer cylinder, a ram tube slidable in said outer cylinder, a closure member fixed to the inner end of the ram tube, said closure member defining in conjunction with the ram tube a low pressure reservoir for hydraulic liquid and in conjunction with the outer cylinder a variable volume pressure chamher, a conduit disposed co-axially within the ram tube, said conduit opening from the pressure chamber and extending towards the outer end of the ram, release valve means situated adjacent the outer end of the ram, said release valve means controlling return flow from said conduit to the reservoir, and pump means mounted in the ram tube for transferring liquid under pressure from the reservoir to the chamber, said pump means comprising large and small area annular pistons disposed concentrically between the conduit and the ram tube, reciprocating drive mechanism operative in common upon said large and small area pistons, and pressure-responsivc means adapted to terminate the pumping action of the large area piston upon the attainment of a predetermined pressure in the pressure chamber.

2. A hydraulic pit prop comprising an outer cylinder, a ram tube slidable in said outer cylinder, a closure member fixed to the inner end of the ram tube, said closure member defining in conjunction with the ram tube a low pressure reservoir for hydraulic liquid and in conjunction With the outer cylinder a variable volume pressure chamber, a conduit disposed co-axially within the ram tube, said conduit opening from the pressure chamher and extending towards the outer end of the ram, release valve means situated adjacent the outer end of the ram, said release valve means controlling return flow from said conduit to the reservoir, and pump means mounted in the ram tube for transferring liquid under pressure from the reservoir to the chamber, said pump means comprising a small area piston of tubular form mounted slidably on the conduit, a cylinder for said small area piston formed in the ram tube closure member, a large area annular piston slidably fitting the bore of the ram tube, reciprocating drive mechanism operative in common upon said large and small area pistons, and pressure-responsive means adapted to terminate the pumping action of the large area piston upon the attainment of a predetermined pressure in the pressure chamber.

3. A hydraulic pit prop as in claim 2, wherein the reciprocating drive mechanism comprises a slide block mounted on the conduit adjacent its outer end, means for reciprocating said slide block on the conduit, a connecting tube disposed around the conduit, said tube forming a drive connection between the slide block and the small area piston.

4. A hydraulic pit prop as in claim 3, comprising also a lost-motion drive mounting for said large area piston provided by axially spaced shoulders formed on said connecting tube, an inlet passage extending from one side of said large area piston to the other, one of said shoulders forming in conjunction with said large area piston a clack valve which is operative to close said inlet passage upon the working stroke of the pump.

References Cited in the file of this patent UNITED STATES PATENTS 2,621,631 Dowty Dec. 16, 1952 

